ALLOYING EFFECTS ON THE ELECTRONIC-STRUCTURES OF LANI5 CONTAINING HYDROGEN-ATOMS

The electronic structures of LaNi5 intermetallic compounds containing a variety of alloying elements were investigated by the DV-X alpha clu ster method in order to understand the effects of alloying on the hydr ogen absorption and desorption characteristics of these compounds. It was found that hydrogen atom made a stronger chemical bond with Ni ato ms than with La atoms in pure LaNi5. The bond strengths between hydrog en and Ni (or La) atoms were scarcely influenced by alloying, despite the fact that hydriding and dehydriding characteristics are greatly mo dified by the addition of alloying elements. On the contrary, both the Ni-Ni and the La-Ni atomic interactions were greatly affected by allo ying. It was shown that the ratio of the La-Ni bond order to the Ni-Ni bond order correlated well with experimental data of dissociation pre ssures. This correlation was also found in other compounds, YNi5 and C aNi5. It was concluded that the strengths of the chemical bonds betwee n the constituent atoms determined the essential features of the hydro gen absorption and desorption characteristics of the ANi(5)-type inter metallic compounds. Copyright (C) 1996 Elsevier Science Ltd.